By early 1968, the Do 31E was flying the full flight profile: vertical take-off and landing, plus high-speed flight at speeds of up to Mach .67. Another American pilot, Drury Wood, a Marine veteran of World War II and Korea, was responsible for the test work. NASA even joined in the test effort.

The Do 31E proved the concept of a VTOL jet-lifter, and both West Germany and the United Kingdom backed the promising airplane.

But by the end of the 1960s and NATO’s shift to Flexible Responsedoctrine—which de-emphasized massive nuclear retaliation—the military need for a VTOL transport plane diminished.

Operating costs for the experimental plane were also prohibitively high. With no fewer than 10 engines, the Do 31E was a heavy and complex gas-guzzler, and stability would be compromised if even one engine were to fail.

Another factor in the demise of the Do 31E was disinterest from the U.S. Air Force, which saw little urgency in distancing its operations from vulnerable air bases.

At one time, Dornier had high hopes that aircraft might be adopted as a commercial regional airliner, buzzing office workers from city to city. But this was never likely. Not only would city-center VTOL planes never have been safe enough or practical, but in common with its VTOL fighter cousins, the Do 31E was ear-splittingly loud.

VAK 191B

The Do 31E was not the end of West Germany’s brief fascination with VTOL. In late 1961, the NBMR-3 requirement prompted design work on yet another new V/STOL fighter, as a replacement for the Fiat G.91.

The G.91 was a conservative design that NATO had selected as a standard lightweight strike fighter in 1958, but only West Germany and Italy operated it in this role.

In mid-1963, the two countries joined forces on the VAK 191B. To power the plane, the German and Italian designers selected a single Rolls-Royce RB.193 lift/cruise engine—with four vectored nozzles in the center fuselage—and two RB.162 lift jets, one in front and one behind the main engine.

Work began in 1965.

Even before it had flown, however, the VAK 191B fell victim to Flexible Response. Low-level nuclear strike was no longer the priority for NATO, and war planners began to conceive a future conflict in which airfields might survive the initial atomic onslaught.

With this, the VAK 191B was reduced in priority from a potential 1,000-aircraft program to little more than a test project.

In 1968, Italy left the program. And in the same year, the United Kingdom, Germany and Italy created the Multi-Role Combat Aircraft (later the Panavia Tornado), putting the final nail in the VAK 191B’s coffin.

It was not until April 1970 that the VAK 191B took to the air, and a free hover only took place in September 1971. Two more flying prototypes followed, and the flight envelope was gradually expanded to include transition from vertical takeoff and landing to high-speed level flight in October 1972.

By the end of the year, funding had been cut off entirely.

The VAK 191B was also hardly practical, with shortcomings in terms of thrust, payload and agility—a product of its relatively tiny main wings.

VFW-Fokker, which ended up with responsibility for the project, had advanced derivatives on the drawing board, including a supersonic version (in its original guise, the VAK 191B topped out at Mach 0.96). They were never to be.

One more failed entrant in NBMR-3 was a little-known joint U.S. and German project, pursued by Republic Aviation and Fokker. Inspired by the Harrier, this new design also used a lift/cruise engine, but combined with separate lift engines and a variable-geometry “swing wing.”

The two companies attempted to refine the design as the Advanced Vertical Strike, to be powered by the radical Rolls-Royce/Allison XJ99. This engine offered an incredible thrust-to-weight ratio of twenty to one. But all in all, AVS was “so complicated that it could hardly have been considered a practical proposition” wrote aviation author Bill Gunston.

Not surprisingly, AVS found no interest and was swiftly sidelined.

After much initial promise, the dream of finding freedom from airfields had come to an abrupt end at the behest of the NATO planning committees. West Germany would continue to operate its aircraft from long runways, leaving them at great risk for the rest of the Cold War.

More broadly, with the exception of the Harrier, no other fixed-wing VTOL aircraft has found true success. Now it’s down to the F-35B to repeat this rare achievement, and avoid the fate of the Harrier’s forgotten Cold War rivals.

Image: Wikipedia.